This invention pertains to the field of weft knitting machines utilizing independent needles. It is directed to a new and useful device for reliably sensing needles having broken heads and then quickly shutting down the operation of such machines. During the operation of weft knitting machines, the needles are subject to substantial stresses as a result of which they may be broken or otherwise damaged. When this occurs, faults occur in the fabric which is in the process of being knit by the needles. Occasionally, machine damage also occurs. The knitting of sliver high pile fabrics on conventional open top circular knitting machines is particularly hard on the needles. Broken needle heads frequently occur as the result of needle stresses encountered in that type of knitting.
Various types of faulty or broken needle detection devices have been known to and used in the art. None, however, have combined the advantages of simplicity, economy of manufacture, reliability in use and immediacy of operation in the detection of broken needles and the shutting down of the knitting machine. This is particularly true in respect to sliver knitting, where fly loss and the unusual stresses imposed on the knitting needles present several problems. Electronic, photoelectric and magnetic broken or faulty needle detection devices have been utilized, but all of them have proven to be highly expensive and of doubtful reliability. Magnetic needle detection devices also suffer from a tendency toward oversensitivity, whereas photoelectric needle detection devices have proven to be generally unsatisfactory in sliver high pile knitting due to the interference of the fly with the light beam.